Unit 4: Transport across membranes Flashcards
What is the structure of a cell membrane described by the fluid mosaic model?
Phospholipid bilayer with a fluid consistency, with proteins scattered just outside or within the membrane to form a mosaic pattern.
The polar head of phospholipid faces outside and inside of the cell where water is, and the nonpolar tails face each other.
Cholesterol function
Type of lipid (steroid) found in animal cell membranes; stiffens and strengthens the membrane to regulate its fluidity.
Peripheral vs Integral protein
i) Peripheral: A small part of the protein held to the inside of the membrane by cytoskeletal filaments
ii) Integral: The whole protein molecule that is embedded into the membrane but moves laterally back and forth.
Glycoprotein vs Glycolipid
Both phospholipid and proteins can have attached carbohydrate chains
i) Protein + Carbohydrate chain = Glycoprotein
ii) Phospholipid + Carbohydrate chain = Glycolipid
Different functions of the membrane proteins (5 types)
- Channel protein: Allows particular molecules or ions to cross the plasma membrane freely
- Carrier protein: Selectively interacts with specific molecules or ions so that it can cross the membrane
- Receptor protein: Shaped in a way that allows a specific molecule to bind to it, such as hormones or growth factors.
- Enzymatic protein: Catalyzes specific reactions. i.e., proteins found in the small intestine catalyze digestive reactions
- Cell recognition protein: The carbohydrate chains attached to proteins function as cell identification markers.
Movements across the membrane: Diffusion
Movement of a solute from an area of high concentration to low concentration. The molecules are said to be following their concentration gradient (high -> low) and continues to move until the particles are distributed evenly about the solvent.
Passive movement: no membrane, carrier, or ATP required.
Factors that affect the rate of diffusion in a liquid/gas (5)
i) Concentration gradient: The greater the concentration gradient, the faster the rate of diffusion
ii) Temperature: higher temperature = faster rate of diffusion
iii) Particle size: the smaller the particle = faster rate of diffusion
iv) Particle shape: Some particles are more streamlined than others and can fit between other particles easier
v) Electrical charge: Non-polar molecules diffuse faster in non-polar solutions and polar molecules diffuse faster in polar solutions
Factors that affect the rate of diffusion across a membrane (7)
All of the factors that affect liquid/gas +
i) Number of pores/carrier proteins/channel proteins: The more openings that are present for a particular molecule, the more of that substance that can cross the membrane
ii) Pressure: The greater the pressure gradient, the faster the rate of diffusion. i.e., the greater the osmotic pressure the faster the water will diffuse across the membrane
iii) Hormonal effects: Hormones such as insulin affects whether or not a substance can access the appropriate carrier to cross the membrane
iv) Lipid solubility: Small non-polar molecules can diffuse naturally across the membrane as they are lipid soluble
v) Cyclosis: Cyclical movement of the cytoplasm in some cells that increase the concentration gradient across the membrane
vi) Membrane permeability: One cell may allow a particular molecule while another cell may not. Cells can also change their permeability depending on its needs.
Movements across the membrane: Osmosis (Osmotic pressure)
Special type of diffusion, where water moves across a selectively permeable membrane due to concentration differences. Membrane is required, but no carrier or ATP required.
The membrane will allow water to pass through until concentration is level, but not allow the solute to pass through.
Osmotic pressure is the force that causes water to move from high concentration of water to low
Isotonic solutions and their effect on cells
Two solutions with equal concentrations of solute to solvent.
Cells placed in isotonic solutions mean the percentage of solute and the concentration of water both inside and outside the cell are equal -> No gain or loss of water.
Hypotonic solutions and their effect on cells
Solution with the lesser amount of solute compared to another solution.
When a cell is placed in hypotonic solutions, water enters the cell as there is higher concentration of water outside the cell than inside -> Gain of water
What happens to animal and plant cells when placed in hypotonic solutions?
- Animal cells in hypotonic solution expand and sometimes burst due to the buildup of osmotic pressure. Lysis is used to refer disrupted cells due to this.
- Plant cells in hypotonic solution experiences turgor pressure, where the central vacuole of the cell expands due to the gain of water and pushes the membrane against the cell wall. The cell does not burst due to the rigidity of the cell wall
Hypertonic solutions and their effect on cells
Solution with the greater amount of solute compared to another solution.
When a cell is placed in hypertonic solutions, water leaves the cell as there is higher concentration of water inside the cell than outside -> Loss of water
What happens to animal and plant cells when placed in hypertonic solutions?
- Animal cells in hypertonic solutions shrink or shrivel due to the loss of water. The term crenation refers to cells in this condition.
- Plant cells in hypertonic solutions experience plasmolysis, where the central vacuole loses water and the cell membrane pulls away from the cell wall, shrinking the cytoplasm.
Movements across the membrane: facilitated transport
Another type of passive transport that allows molecules to pass through a membrane through the concentration gradient. Carrier protein is needed as these molecules cannot be diffused into the cell by itself.
